1. Field of the Invention
The present invention relates to an analog buffer, and more particularly, to an analog buffer with voltage compensation mechanism.
2. Description of the Related Art
Because liquid crystal display (LCD) devices are characterized by thin appearance, low power consumption, and low radiation, LCD devices have been widely applied in various electronic products for panel displaying. The operation of an LCD device is featured by varying voltage drops between opposite sides of the liquid crystal cells of the LCD device for twisting the angles of the liquid crystal molecules in the liquid crystal cells so that the transparency of the liquid crystal cells can be controlled for illustrating images with the aid of the light source provided by a backlight module.
In general, the LCD device comprises a plurality of pixel units, a plurality of data lines and a source driver. The source driver comprises a plurality of source driving circuits. The source driving circuits perform latching operations, level shifting operations, digital-to-analog converting operations and analog signal buffering operations on the digital image data signals inputted to the LCD device for generating a plurality of analog signals. Each source driving circuit is coupled to a corresponding data line for writing the generated analog signals into corresponding pixel units.
Accordingly, the analog buffer of each source driving circuit for performing the analog signal buffering operation functions as a key element for writing the generated analog signals into corresponding pixel units. With the aid of the analog buffers having enhanced driving ability for performing high-speed and accurate buffering operations, the LCD device is capable of providing high display quality. That is, the display quality of the LCD device is corresponding directly to the performance of the analog buffers. Furthermore, the source driver is installed with lots of analog buffers in that each source driving circuit should be installed with an individual analog buffer, and therefore a significant part of the layout area of the LCD device is required for accommodating the analog buffers. For that reason, simplified designs of the analog buffer and related control circuit without degrading the driving performance are required for realizing advanced low-cost LCD devices having thinner appearance.
FIG. 1 is a schematic diagram showing the circuit of a conventional analog buffer for use in an LCD device. As shown in FIG. 1, the analog buffer 100 comprises an N-type metal-oxide-semiconductor (MOS) transistor 111, a P-type MOS transistor 112, a plurality of capacitors 121-124, a plurality of switches 131-142, and two current sources 181 and 182. The analog buffer 100 is utilized to perform the analog signal buffering operation on an input voltage Vin for generating an output voltage Vout for charging the pixel capacitor Cpixel. However, the aforementioned conventional analog buffer is operated based on a variety of complicated control signals for controlling on/off states of the switches. Also, extra current control signals are required for controlling the current sources of the conventional analog buffer. That is, the circuit operation of the conventional analog buffer should be performed with the aid of complicated control circuits for generating the complicated control signals. In summary, the conventional analog buffer cannot meet the demand for designing advanced low-cost LCD devices having thinner appearance.